On-chip optical communications and optical interconnects are the subject of substantial research and interest in the field of micro- and nano-photonics. Many in the industry anticipate light replacing electrons as global interconnects on high-performance chips. However, photonic waveguides generally require very high precision in order to reduce scattering losses and can be difficult to fabricate.
FIG. 1 illustrates a cross-sectional view of a typical photonic crystal slab waveguide. In such devices, a slab of silicon 10 can be perforated with holes 12 across selected areas of the slab to form a guiding layer 14. Certain areas of the silicon slab can be left intact with no perforations. The slab thickness is generally chosen close to half the wavelength of propagating light in the guiding layer such that the waveguide is single mode. The propagating mode 16 exhibits a typical Gaussian wave form where the field evanesces outside of the guiding layer and has a Gaussian bell curve shape within the guiding layer. These devices also require a low refractive index substrate 18 between the guiding layer and the underlying substrate 20. Typically, these low refractive index substrates can be difficult and expensive to manufacture, especially those with refractive index approaching one. Substrates having higher refractive indices allow the propagating mode to leak into the substrate increasing loss. A number of efforts have focused on improving the quality and properties of these low index substrates with moderate to limited success. As such, photonic waveguide devices with reduced losses and increased ease of manufacture continue to be sought.